Rubber tires are often prepared in a manufacturing process by first building a tire carcass and then building a tire tread over the carcass. The tire tread is conventionally applied to the tire carcass as an uncured rubber strip, which may be contoured, where the uncured rubber strip is wound around the carcass with the ends of the uncured rubber strip meeting to form a splice. The ends of the uncured rubber tread strip for a new tire are usually skived, or cut, at an angle to permit the ends of the uncured rubber strip to overlay (overlap) each other to some degree, instead of a straight cut in a form of a butt splice, to form a splice comprised of joining the ends of the uncured rubber tread strip. Such procedural tire tread fabrication utilizing a splice to join the ends of an uncured tread rubber strip is well known to those having skill in such art.
For such practice, it is desired that the ends of the uncured rubber tread strip necessarily have a degree of tackiness, sometimes referred to as building tack, so that the tread splice holds together after its construction and is suitable for subsequent tire molding and curing. However, for such splice, the ends of the uncured rubber tread strip sometimes do not have sufficient desirable natural building tack for such purpose so that a rubber cement is sometimes applied to the surface of at least one end of the rubber strip to aid in promoting building tack. For example, see U.S. Pat. No. 8,143,338.
Providing such building tack for the ends of such uncured rubber strip is considered to be significantly more challenging where the rubber composition of the strip contains a high content of precipitated silica, namely a hydrophobated precipitated silica, where the content of such silica in the rubber composition can significantly exceed the content of the rubber (elastomer) itself. Such high content of hydrophobated silica is considered to reduce the building tack of the uncured rubber composition.
In practice, precipitated silica (an amorphous synthetic silica) is hydrophilic in nature and thereby challenging to efficiently blend with and disperse within diene-based elastomers unless it is made more hydrophobic in nature as is understood to be well known to those having skill in such art. Such hydrophilic precipitated silica may, for example, be hydrophobated in situ within the rubber composition or may be pre-hydrophobated prior to its addition to a rubber composition. For example, see U.S. Pat. Nos. 4,474,908, 5,780,538, 6,127,468 and 6,573,324
The precipitated silica may be hydrophobated for example, with one or more hydrophobation promoting compounds which are reactive with hydroxyl groups (e.g. silanol groups) contained on the precipitated silica which may be comprised of, for example one or more of alkoxysilane, alkylsilane, halogenated alkylsilane, and silica coupling agents such as, for example, bis(3-trialkoxysilylalkyl)polysulfide containing an average in a range from about 2 to about 4 connecting sulfur atoms in their polysulfidic bridges (e.g. comprised of bis(3-tri ethoxysilylpropyl)polysulfide, or an organoalkoxymercaptosilane.
As indicated, it is understood that such hydrophobation promoting compounds rely, at least in part, upon reaction of its silane or siloxane moiety with hydroxyl groups (e.g. silanol groups) on the precipitated silica. For such reaction, it is understood that not all of the hydroxyl groups of the precipitated silica become chemically interacted with such compounds and that therefore a portion of the hydroxyl groups on the precipitated silica remain as available hydroxyl groups for further chemical reaction(s).
Historically, as previously indicated, a rubber cement coating is often applied to the face, or end surface, of at least one of the opposing ends of an uncured tire tread rubber strip to promote building tack and the ends joined to form a splice thereof with the resulting promoted building tack between the ends of the tread strips relied upon to hold the splice together during the tire building process. Organic solvent based and water based cements have been used for such purpose, although water based cements are normally expected to take an extended period of time to dry, normally for the water to evaporate, prior to joining the ends of the uncured rubber strips.
For this invention, it is desired to undertake providing building tack to the ends of such uncured rubber tread strip which contains a high content of particulate hydrophobated precipitated silica, namely an uncured tread rubber strip comprised of a rubber composition having a hydrophobated precipitated silica content at least about 70 weight percent, alternately at least about 105 weight percent and alternately at least about 175 weight percent based on its rubber content.
On such basis, then, it is desired for the building tack promoting cement to interact with the hydrophobated silica as well as the elastomer of the rubber composition of the uncured rubber strip, particularly with the ends of the uncured rubber strip joined together to form a splice.
For this invention, then, as indicated, it is desired to undertake providing building tack to ends of an uncured rubber tread strip with a water based composition to promote building tack for the splice and thereby forming a splice, namely a spliced uncured rubber tread strip, with a water based composition where the rubber composition of the uncured tread strip contains a high content of particulate hydrophobated precipitated silica, namely where such hydrophobated silica significantly exceeds the rubber content of the rubber composition.
In the description of this invention, the terms “rubber” and “elastomer” may be used interchangeably, unless otherwise prescribed. The terms “rubber composition,” “compounded rubber” and “rubber compound” are used interchangeably to refer to rubber which has been blended or mixed with various ingredients and materials and such terms are well known to those having skill in the rubber mixing or rubber compounding art.